The present invention relates to a method of manufacturing a multi-layered wiring substrate having vias for electrically connecting upper and lower conductor wiring layers which sandwich a dielectric film.
In a conventional multi-layered wiring substrate using an organic dielectric film, vias for electrically connecting upper and lower conductor wiring layers which sandwich a dielectric film are formed by the following method. That is, after a photosensitive polyimide resin is applied to an entire surface of a substrate including a conductor wiring layer, exposure and development are performed through a predetermined mask to form via-holes. Then, after the photosensitive polyimide resin is cured, a polyimide-based conductive resin is embedded in the via-holes. The polyimide-based conductive resin is cured to form vias.
As described above, in a via formation means by the method of manufacturing a conventional multi-layered wiring substrate, first, a dielectric film having via-holes must be formed. However, it is considerably difficult to uniformly form these via-holes in an entire surface of the substrate. In particular, when the thickness of the dielectric film is increased, it is difficult to control the shapes of the via-holes. The formation state of the via-holes is insufficient, or the dielectric film is largely removed to form a reverse-tapered via-holes. In all cases, disconnection of the conductor wiring (pattern) in via portions is caused. When the thickness of the dielectric film is small, the via-hole shapes are easily controlled, and uniformity of the via-hole shapes in a single substrate is improved. However, reliable insulation between lower and upper conductor wiring layers cannot be achieved. In order to insulate the layers without failure, the thickness of the dielectric film need be increased. Thus, the method of manufacturing the conventional multi-layered wiring substrate has a drawback that it is difficult to obtain fine shapes of the via-holes in a dielectric film having a predetermined thickness.